Internet protocol (“IP”) telephony and IIP multimedia networks employ several protocols to setup and manage calls and sessions. One of the most widely adopted protocols for IP-based signaling is the Session Initiation Protocol (“SIP”). SIP is used, for example, for initiating new calls and sessions, manipulating call paths, and enabling the association of services with users regardless of their point of connection in the network. These are just a few areas of application of the SIP.
The increasing use of SIP has spurred development and introduction of numerous services with SIP interfaces for user and network access. This approach makes sense as the number of SIP-capable devices proliferates in IP networks. The use of SIP as an interface assures that a “customer” and a “server” can rely on a common and widely used method for exchanging information.
One general category of service relevant to SIP capabilities is directory services. SIP-based services, and other IP-signaling protocols, are generally lacking in methods for directory and directory-related services. For example, current SIP standards require that a destination identifier used in SIP messages must be an exact match to a specific identifier of the called party. This requirement eliminates the possibility of providing searches for ambiguous destination identifiers.
In particular, when a SIP message carries a destination identifier, such as a Uniform Resource Locator (“URL”), it must be an exact match to an identity or symbolic name that can be mapped to an IP address for a connection to occur. For example, the URL “John_Doe@3Com.com” used as the destination identifier in a SIP message must exactly match a character string that can be resolved, e.g., by a database lookup, to the routable IP address of the intended recipient. When the SIP message is received by a redirect server, the server resolves the message if an exact match to the destination identifier can be found in a mapping database, and responds to the sender with the proper routing information. If an exact match cannot be found, a response message is sent that indicates that the message is unroutable. Therefore, if a database lookup fails to yield an exact match to “John_Doe@3Com.com,” the message would be deemed unroutable. This limits the utility of a SIP-based directory service to finding routes only when a caller (origin of the message) knows the exact destination identifier.